I have been trying to find out if it's possible to travel within Switzerland on the Tgv with a gemeinde tageskarte. Can anyone help me? I think it is but don't want to wait until I am on the train to find out.

Yes you can. I have used the Gemeinde Tageskarte on the TGV, Railjet, ICE and the Italian trains for travel within CH without any problems. More often than not, there is an SBB Ticket Inspector with the foreign ticket inspectors.